Answer:
decrease, decrease
Explanation:
By using antimalarial drugs in order to prevent malaria, the frequency of the sickle cell allele decreases in both areas where malaria is endemic and the areas where no incidence of malaria occurs because there is no necessity of sickle cell allele in the population to prevent malarial disease. Sickle cells have high significance in prevention of malarial diseases so when there is no malaria happens in the population so there is no need for it and the allele slowly removed from the population and decrease occurs in its frequency.